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Summary Peroral endoscopic myotomy (POEM) is a safe and effective minimally invasive treatment for achalasia. Postoperative reflux rates remain high. The functional luminal imaging probe (FLIP) allows intraoperative measurement of lower esophageal distensibility during POEM. In theory, this enables a tailoring of myotomies to ensure adequate distensibility while minimizing postoperative reflux risk. Two prospectively collected POEM databases were analyzed from two UK tertiary upper GI centers. The operators in each center used FLIP measurements to ensure adequate myotomy. Outcome measures included Eckardt score (where

Current evidence for oxygenated environments in the Mesoarchean is limited to the shallowest marine and fluvio-lacustrine settings. It is not until the Neoarchean that signs of oxygenated surface waters above outer shelf and basinal depositional environments become evident. In order to further explore the Mesoarchean redox landscape for signs of basinward surface water oxygenation, we present nitrogen and carbon isotope ratios from the turbiditic Mosquito Creek Formation of the Nullagine Group (∼2.9 Ga). The δ15N and δ13Corg values are invariant around −1.8‰ and −32‰ respectively throughout a 70 m section of drill-core, suggesting an ecosystem dominated by nitrogen fixers (anaerobic nitrogen cycling) and CO2 fixation by the Calvin Cycle. When compared with other Archean isotopic data, these results (i) provide further evidence that the Mosquito Creek Formation was deposited in a marine basin, and (ii) contain δ15N values that highlight the prevalence of nitrogen fixation by Mo-nitrogenase and the dearth of aerobic nitrogen metabolisms in the Mesoarchean.

We report in situ quadruple sulfur isotope analysis (32S, 33S, 34S and 36S) of a pyritized microbial mat from the ∼3480 Ma Dresser Formation, Pilbara Craton, Western Australia. These data yield positive δ34S and Δ33S, indicative of sulfur sourced from a pool with similar character as the putative atmospheric elemental sulfur channel of Pavlov and Kasting (2002). Contrary to previous data from the Dresser Formation, however, this pyrite is heavily depleted in 36S with a Δ36S/Δ33S slope of c. −3.6, much steeper than slopes typically seen in other early Archean rock successions (Δ36S/Δ33S ≈ −1) which suggests either a different atmospheric signature for deposited S or a different pool altogether. Significant micro-scale isotopic heterogeneity is observed within the microbial mat (δ34S = +1.6‰ to +6.7‰; Δ33S = +0.4‰ to +2.6‰; Δ36S = −3.1‰ to −8.1‰), implying a role for microbial S metabolism. While metabolic S cycling has been shown to shift Δ36S to lower values, microbial metabolization of S does not appear sufficient to account for the full range of Δ36S. We conclude that the isotopic composition of the pyrite was controlled by the relative proportions of mass independently fractionated (MIF) S0 and sulfate-derived sulfur incorporated into polysulfide pyrite precursors during reactions in the microbial mat. The dominance of the MIF-S0 isotopic signature (+δ34S, +Δ33S, −Δ36S) indicates that contributions from the sulfate-derived sulfur pool were relatively small, consistent with low concentrations of sulfate in Archean seawater, and that contributions from a non-sulfate pool were significant. Micro-scale isotopic heterogeneity in the pyrite points to mixing between the two sulfur pools in selected micro-environments within the microbial mat. The particularly negative Δ36S observed here reveals a 3480 Ma sulfur reservoir with novel Δ36S/Δ33S chemistry whose significance now requires further investigation.

The 1.88-Ga Gunflint biota is one of the most famous Precambrian microfossil lagerstätten and provides a key record of the biosphere at a time of changing oceanic redox structure and chemistry. Here, we report on pyritized replicas of the iconic autotrophic Gunflintia–Huroniospora microfossil assemblage from the Schreiber Locality, Canada, that help capture a view through multiple trophic levels in a Paleoproterozoic ecosystem. Nanoscale analysis of pyritic Gunflintia (sheaths) and Huroniospora (cysts) reveals differing relic carbon and nitrogen distributions caused by contrasting spectra of decay and pyritization between taxa, reflecting in part their primary organic compositions. In situ sulfur isotope measurements from individual microfossils (δ 34 S V-CDT +6.7‰ to +21.5‰) show that pyritization was mediated by sulfate-reducing microbes within sediment pore waters whose sulfate ion concentrations rapidly became depleted, owing to occlusion of pore space by coeval silicification. Three-dimensional nanotomography reveals additional pyritized biomaterial, including hollow, cellular epibionts and extracellular polymeric substances, showing a preference for attachment to Gunflintia over Huroniospora and interpreted as components of a saprophytic heterotrophic, decomposing community. This work also extends the record of remarkable biological preservation in pyrite back to the Paleoproterozoic and provides criteria to assess the authenticity of even older pyritized microstructures that may represent some of the earliest evidence for life on our planet.

Komatiites occur in many Archean greenstone belts and host significant Ni sulfide ore deposits. Establishing the stratigraphy and the control that stratigraphy has on the emplacement and morphology of ultramafic magmatism is crucial in understanding Archean geodynamic environments and in targeting for Ni sulfide mineralization within these environments. The ~2.9 Ga Lake Johnston greenstone belt, in the southern portion of the Youanmi Terrane of Western Australia, contains komatiite flows and related subvolcanic intrusions, mafic volcanic rocks, felsic volcanic rocks, banded iron formation, and sedimentary rocks. The stratigraphic sequence is intact, preserving original sedimentary and igneous textures and contact relationships, despite being overturned and variably deformed. This study proposes that the lithostratigraphic succession and ultramafic intrusions identified within the Lake Johnston greenstone belt record a transition from arc- to plume-dominated magmatism, accompanied by the establishment of a banded iron formation-dominated sedimentary basin. It is proposed that the rheological contrast between the felsic volcanic unit and overlying banded iron formation acted as a stratigraphic barrier, trapping ascending ultramafic magmas. The stratigraphic barrier inhibited the upward ascent of ultramafic magma causing the development of a subvolcanic magma chamber. Magma trapped beneath the banded iron formation progressively inflated and spread out along the contact, until overpressuring breached the banded iron formation and magma escaped, forming the overlying extrusive komatiites. Both the geodynamic and lithologic transitions gave rise to favorable substrate rock units and an ideal tectonic setting for formation of komatiite-hosted Ni sulfide ores.

The Agnew-Wiluna greenstone belt of Western Australia is the largest komatiite-hosted nickel sulfide belt in the world and contains two world-class Ni-Cu-(PGE) deposits and a host of smaller deposits. This study focuses on the broader scale geology of this greenstone belt in order to understand the key controls on the genesis of the komatiite-hosted Ni-Cu-(PGE) deposits, with specific focus on camp to district controls. We apply multiple sulfur isotopes to this geologic framework and conclude not only that the addition of crustal sulfur is a prerequisite for ore genesis in komatiite systems, but above all that the sulfur required to generate world-class deposits is most likely derived from barren volcanic massive sulfide lenses, which are spatially and genetically associated with felsic volcanic and volcaniclastic sequences that were emplaced coevally with large komatiitic sills and channelized lava flows. Multiple sulfur isotope data can be utilized in exploration at the deposit to district scales. At the deposit scale, the spatial pattern of mass-independent S isotope values (Δ 33 S) provides crucial insight into the identification of proximal high-grade and high-tenor ores in mineralized systems. In fact, sulfur data reflect the assimilation process that occurred upon komatiite emplacement, whereby hot turbulent magma thermomechanically eroded and assimilated exhalative sulfides spatially located close to vent with negative to near zero Δ 33 S values, whereas less turbulent flows interacted with distal sulfidic shales having Δ 33 S values above 0 per mil. Accordingly, the spatial variation of multiple sulfur isotope values in magmatic sulfides and associated host rocks may be utilized as a vector towards high-grade ores of poorly known systems. At the district scale, rather than ascertaining what controls the distribution of komatiite-hosted Ni-Cu-(PGE) deposits, the appropriate question to ask is what controls the distribution of country rock sulfides, considering that exhalative sulfides may be crucial to ore genesis in komatiite systems. We propose that felsic lava domes unambiguously mark their vents and can be directly mapped or inferred from gravity data. This work provides the first step in identifying district-scale control on komatiite-hosted Ni-Cu-(PGE) deposits. This is the scale that has high impact on exploration for new komatiite-hosted nickel sulfide belts globally.

Within medicine, the concept of reflection is becoming a fashionable component of lifelong learning and revalidation. It remains poorly practised and misunderstood with scant guidance available on the benefits, methodology or founding principles. Using the intrinsically unsafe state of anaesthesia as a clinical example, the stages of reflection are discussed in context. Components of metacognition (‘thinking about thinking’) are also clinically contextualised. Barriers to reflection and metacognitive practice are discussed, emphasising the need for medical regulators to deliver clarity on the processes they propose clinicians to use to reflect. Opportunities to promote reflective practice from clinicians’ existing working patterns are proposed.

International audience; The enrichment of redox-sensitive trace metals in ancient marine sedimentary rocks has been used to determine the timing of the oxidation of the Earth's land surface1,2. Chromium (Cr) is among the emerging proxies for tracking the effects of atmospheric oxygenation on continental weathering; this is because its supply to the oceans is dominated by terrestrial processes that can be recorded in the Cr isotope composition of Precambrian iron formations3. However, the factors controlling past and present seawater Cr isotope composition are poorly understood. Here we provide an independent and complementary record of marine Cr supply, in the form of Cr concentrations and authigenic enrichment in iron-rich sedimentary rocks. Our data suggest that Cr was largely immobile on land until around 2.48 Gyr ago, but within the 160 Myr that followed--and synchronous with independent evidence for oxygenation associated with the Great Oxidation Event (see, for example, refs 4-6)--marked excursions in Cr content and Cr/Ti ratios indicate that Cr was solubilized at a scale unrivalled in history. As Cr isotope fractionations at that time were muted, Cr must have been mobilized predominantly in reduced, Cr(III), form. We demonstrate that only the oxidation of an abundant and previously stable crustal pyrite reservoir by aerobic-respiring, chemolithoautotrophic bacteria could have generated the degree of acidity required to solubilize Cr(III) from ultramafic source rocks and residual soils7. This profound shift in weathering regimes beginning at 2.48 Gyr ago constitutes the earliest known geochemical evidence for acidophilic aerobes and the resulting acid rock drainage, and accounts for independent evidence of an increased supply of dissolved sulphate8 and sulphide-hosted trace elements to the oceans around that time1,9. Our model adds to amassing evidence that the Archaean-Palaeoproterozoic boundary was marked by a substantial shift in terrestrial geochemistry and biology.

The Agnew–Wiluna greenstone belt in the Yilgarn Craton of Western Australia is the most nickel-sulfide-endowed komatiite belt in the world. The Agnew–Wiluna greenstone belt contains two mineralised units/horizons that display very different volcanological and geochemical features. The Mt Keith unit comprises >500 m-thick spinifex-free adcumulate-textured lenses, which are flanked by laterally extensive orthocumulate-textured units. Spinifex texture is absent from this unit. Disseminated nickel sulfides, interstitial to former olivine crystals, are concentrated in the lensoidal areas. Massive sulfides are locally present along the base or margins of the lenses or channels. The Cliffs unit is locally >150 m thick and comprises a sequence of differentiated spinifex-textured flow units. The basal unit is the thickest, and contains basal massive nickel-sulfide mineralisation. The Mt Keith and Cliffs units display important common features: (i) MgO contents of 25–30% in inferred parental magmas; and (ii) Al/Ti ...

Early Ore Formation Ore deposits contain most of the world's metal resources, from commonly used metals such as iron, to precious and expensive metals such as platinum. Understanding how these ancient deposits form may lead to more efficient metal extraction and give clues about early Earth. Bekker et al. (p. 1086 ) studied sulfur and iron isotopes in 2.7-billion-year old Fe-Ni sulfide deposits from Canada and Australia and found that most of the metal-scavenging sulfur was originally atmospheric in origin. Photochemical reactions in the ancient oxygen-free atmosphere produced sulfide that eventually circulated to the sea floor and mixed with newly erupted komatite magmas. Thus, global surface processes in the oceans, atmosphere, and on continents are geochemically linked to ore-forming processes within Earth.

Banded iron formations (BIFs) have long been considered marine chemical precipitates or, as more recently proposed, the result of episodic density flows. In this study, we examined the mineralogy, petrography and chemistry of the Dales Gorge BIF to evaluate the validity of these models. Microbands reflect a compositionally variable primary precipitation/sedimentation pattern with diagenetic modifications. “Iron-rich” bands are characterized by massive anhedral aggregates and xenomorphic hematite, commonly showing overgrowths of subhedral magnetite with minor apatite and late diagenetic ankerite-Fe dolomite. “Iron-poor” bands consist of fine-grained quartz, siderite and Fe-talc in variable amounts. Amorphous silica, ferrihydrite (precursor of hematite), greenalite and possibly some siderite constitute the primary precipitates, while ankerite-Fe dolomite, Fe-talc and magnetite and the bulk of siderite are secondary mineral phases. Ankerite and Fe-dolomite most likely represent by-products of siderite dissolution and the subsequent reaction of dissolved bicarbonate with Ca, Mg and Fe. Ferroan-talc is thought to be formed from the following reactions: (i) greenalite + chert, and (ii) siderite + chert. Magnetite formed from the conversion of hematite, likely through bacterial Fe(III) reduction. Geochemical mineral analyses show that all the phases have very low concentrations of trace elements with the exception of Ba, As, Cr, Zn and Sr. This partitioning was presumably controlled by both sorptive reactions occurring during primary precipitation in the water column and secondary remobilization during diagenesis. Whole-rock analyses indicate two decoupled sources for BIF and S macrobands. While BIF macrobands have a major hydrothermal influence, data from the S macrobands supports a dominantly mafic provenance. Nonetheless, when all the lithologies (i.e., source rocks, S and BIF macrobands) are evaluated together, continuous geochemical trends can be observed. This suggests that at least part of the precursor material of BIF macrobands was sourced from the same material that gave origin to the S macrobands. Similar relationships are seen in other BIF successions, where the evolution from an ultamafic- to a mafic-dominated upper continental crust is distinctly reflected in BIF compositions through time. Interpretation of this data implies that any model developed to explain BIF deposition must consider: (i) processes involving low-temperature weathering of the continental and ocean basement rocks, mainly (ultra)mafic lithologies; and (ii) high temperature water–rock reactions associated with hydrothermal activity at spreading ridge centers or seamounts. In either case, the influence of the compositional change of the upper continental crust played a major role in the chemical compositions of BIFs through time.

The basal parts of the Higher Himalayan Crystallines (HHC), Lesser Himalayan sedimentary sequences and mylonite zone at the base of Main Central Thrust (MCT) within the NW Himalaya clearly demonstrate anorogenic magmatic signatures at around 1860 Ma, as indicated by SHRIMP U–Pb zircon ages from Bandal granitoids, Kulu–Bajura mylonite and Wangtu granitoids along the Sutlej Valley, Himachal Pradesh. Some of the zircon crystals contain older cores mostly extending back to 2600 Ma. We report for the first time a 3000 Ma old zircon core from Wangtu granitoids, which indicates reworking of ensialic Archaean crust during the assembly of the Columbia Supercontinent between 2.1 and 1.8 Ga. During the Himalayan collisional tectonics, the reworked Archaean and Palaeoproterozoic crust was imbricated and placed adjacent to each other in the Higher Himalayan Crystallines, the Inner Lesser Himalayan window zone and the Kulu–Bajura Nappe. The Himalaya is the youngest evolving active mountain belt in the world, displaying various geodynamic processes and the development of distinct tectonic units (Fig. 1; Gansser 1964; Le Fort 1975; Honegger et al. 1982; Coward et al. 1982; Valdiya 1989; Searle et al. 1993; Thakur 1993; Hodges 2000; Jain et al. 2002; Yin 2006). This highest mountain chain in the world extends laterally for about 2500 km from Nanga Parbat (8126 m, 338150N:748360E) in the west to Namche Barwa (7756 m, 298370N:958150E) in the east and has a width of 250–300 km. The geology of this orogenic belt has been summarized in recent syntheses (Hodges 2000; Jain et al. 2002; Steck 2003; Yin 2006), following an initial attempt by Gansser (1964). These syntheses mostly deal with the Cenozoic collisional tectonics with very little emphasis on the pre-Himalayan history. The pre-Himalayan history has been mainly constrained by the presence of various granitoids, whose ages were assigned from the Proterozoic to Late Cenozoic, based on field relationships, nature of xenoliths, degree of metamorphism, petrographical similarities and structural trends, prior to the application of isotopic dating methods (McMahon 1884; Greisbach 1893; Auden 1935; Wadia 1928, 1957; and others). In the Himalaya, the first radiometric age was reported by Jager et al. (1971) with a Rb–Sr whole-rock isochron for the Mandi Granite, followed by Rb–Sr age determinations by Bhanot et al. (1974, 1975, 1976), Frank et al. (1977), Mehta (1977) and others from the NW Himalaya. These ages clearly indicate the presence of pre-Himalayan granitoids, now metamorphosed to gneiss, and ranging in age from 2.0–0.5 Ga (Singh 2001, 2005; Singh & Jain 2003). These rock bodies are mostly confined to the Higher Himalayan Crystallines (HHC) and the North Himalayan Gneissic Domes. The HHC contain three main types of granitoids ranging in age from 2600 Ma to as young as 2 Ma along distinct zones and can be grouped into a Proterozoic belt, Pan-African belt and the collisionrelated Cenozoic Higher Himalayan Leucogranite (HHL) belt, respectively (see Singh & Jain 2003 for details). The rocks from the basal zone HHC, between the Main Central Thrust in the south and the Vaikrita Thrust in the north, are generally fineto coarse-grained megacrystic gneiss, associated with metasediments and amphibolites, and are the oldest in the Himalaya (Table 1). These are variously called the Iskere gneiss, Kotla and Shang gneiss (in Pakistan), Rameshwar granitoid, Bandal granitoid, Kulu–Bajura mylonitic gneiss, Wangtu Granitic Complex, Naitwar, Hanuman Chatti, Bhatwari, Namik, Gwalda, Chailli, Ghuttu, From: REDDY, S. M., MAZUMDER, R., EVANS, D. A. D. & COLLINS, A. S. (eds) Palaeoproterozoic Supercontinents and Global Evolution. Geological Society, London, Special Publications, 323, 283–300. DOI: 10.1144/SP323.14 0305-8719/09/$15.00 # Geological Society of London 2009. Chirpatiya, Rihee-Ganga, Ramgarh, Almora– Askot–Dhramgarh gneiss (all in India), to the Lingtse, Darjeeling-Sikkim, Bomdila andKalaktang granite gneiss (in NE Himalaya). These bodies are meta-aluminous to peraluminous in composition, with S-type characteristics. They have SiO2 concentrations between 60 and 76% and plot in the Within Plate Granite (WPG) field in the Rb v. YþNb discrimination diagram of Pearce et al. (1984), indicating their anorogenic character (Fig. 2). These data play an important role in the reconstruction of the pre-Himalayan configuration, which has not been attempted prior to Pan-African times (Le Fort et al. 1987). Recently, much attention has been paid to reconstruction of the MesoNeoproterozoic Rodinian supercontinent, but the position of the Himalaya (Greater India) has not been discussed in detail (Dalziel 1991, 1992; Powell et al. 1993; Li et al. 1996; Dalziel et al. 2000). The concept of ‘Greater India’ postulates the northern extension of the Indian sub-continent in the Himalaya (Argand 1924; Veevers et al. 1971, 1975). This configuration was widely accepted in the Gondwana fit of the Indian Plate with the Australian and Antarctica plates, where Greater India was placed next to Western Australia (Powell et al. 1988). A recent synthesis by Ali & Aitchison (2005) details the ‘Greater India’ concept. The Greater India acquires places/gaps north of the Indian Plate containing rocks of presentday Lesser Himalayan Sedimentary Zone and Higher Himalayan Crystallines. The existence of Greater India can be traced back to the pre-Rodinian supercontinent of Columbia in the Palaeoto Mesoproterozoic (Rogers & Santosh 2002; Zhao et al. 2002, 2003; Santosh et al. 2003; Zhao et al. 2004). Between 2.1 and 1.8 Ga, various collisional orogenies took place, as listed by Zhao et al. (2003). Within India, the southern and northern Indian blocks sutured along the c. 1.8 Ga Central Indian Tectonic Zone (Jain et al. 1991; Mazumder et al. 2000). According to the configuration proposed by Zhao et al. (2003), the ‘Greater India’ zone was placed within the plate set-up to the north of the Central Indian Tectonic Zone. Timing also characterizes subduction-related magmatism along the continental margin of the Columbia Supercontinent (Karlstrom et al. 2001; Rogers & Santosh 2002; Condie 2002; Zhao et al. 2002, 2003). Further more, during Mesoproterozoic times (1.6–1.2 Ga), anorogenic anorthosite-magnesite-charnockite granite and rapakivi granites were generated, probably due to an extensive underplating, preceding the breakup of the Columbian Supercontinent (Rogers & Santosh 2002; Zhao et al. 2003) with contemporaneous plate-scale kimberlite emplacement due to plume activity. That resulted in the dispersion of the cratonic blocks of Columbia (Zhao et al. 2002, 2003). The present work reports Palaeoproterozoic U–Pb SHRIMP ages of granite gneiss and mylonite from parts of the Greater Indian crust in the NW Himalaya and assesses its significance for the assembly of the Columbia Supercontinent. Fig. 1. Simplified regional geological map of the Himalaya in plate tectonic framework. SSZ, Shyok Suture Zone; ITSZ, Indus Tsangpo Suture Zone; STDS, South Tibetan Detachment System; MCT, Main Central Thrust; MBT, Main Boundary Thrust. Compiled from published data. S. SINGH ET AL. 284

We present a new lithogeochemical method to target prospective komatiites that may host Ni-Cu-(PGE) deposits. The new methodology is based on the geochemical properties of ruthenium (Ru) and chromium (Cr), elements that are immobile under most conditions; it relies on a restricted number of carefully selected representative samples and is applicable in highly altered terrains. Ruthenium is a platinum-group element (PGE) that exhibits contrasting geochemical behavior in sulfide-saturated and sulfide-undersaturated komatiites. Similarly to other PGEs, Ru shows highly chalcophile behavior in magmas that equilibrate with an immiscible sulfide phase. However, Ru is also compatible in chromite in sulfide-undersaturated systems. If we consider Cr concentration as an index of chromite abundance in chromite-saturated komatiites, we observe that Ru increases or decreases systematically with increasing Cr according to the sulfide saturation state of the magmatic system. In rocks that crystallized from sulfide-saturated melts, Ru contents decrease with increasing Cr. Conversely, in rocks that crystallized from sulfide-undersaturated melts, Ru contents increase with increasing Cr. As a result, on the basis of the Ru-Cr variation it is possible to discriminate whether a komatiite melt equilibrated with a sulfide liquid during crystallization. The strength of this method compared to previous PGE-based lithogeochemical techniques derives from combining the traditional use of the geochemical properties of a highly immobile and chalcophile element that records the ore-forming process (ruthenium) with the occurrence of a mechanically and chemically resistant mineral phase (chromite), which is generally preserved in highly altered komatiites.

Siliciclastic supersequences in the Eastern Goldfields Superterrane are remnants of basins that were linear zones of subsidence between intra-terrane faults. Fluvial deposits record proximal to medial braid-plains. Deep-marine canyon and fan deposits were linked across intra-terrane compartments only by mud-rich deposits. Axial depositional systems dominate, with only minor evidence for slope-aprons, although transverse and axial systems are preserved in some fluvial deposits. Basin development occurred during two stages separated by an inversion event, with the Kalgoorlie Terrane recording change from a fluvial to a deep-marine basin and the Kurnalpi Terrane change from distal to proximal deep-marine facies tracts. Sparse palaeocurrents establish that uplift to the north controlled sediment dispersal. Lithofacies stacking is aggradational, whereas abrupt upwards-change in facies tracts is back-stepping within depositional sequences, and between depositional-sequence sets, but forward-stepping between depositional sequences. The stratigraphic architecture is atypical of synorogenic basins but consistent with a strike-slip regime characterised by pulsed uplift-subsidence, steady-state basin lengthening and subsidence, punctuating catastrophic subsidence and lengthening, and tectonic anchoring. The basins are interpreted to have been similar to graben and half-graben of the Western Anatolian extensional province of Turkey, with linear zones of subsidence developing adjacent to strike-slip, oblique-slip or normal dip-slip faults. Controls on stratigraphic patterns are considered to have been regional rather than at the scale of each basin. The envisaged tectonic setting is similar to projected collision between the Philippine Archipelago west of the Philippine Fault and continental crust of the South China Sea, but the orogenic architecture is similar to that of accreted superterranes in the Canadian Cordillera. Interpreted north- or northwest-convergence between the Burtville Terrane to the east and the ancestral Yilgarn continent to the northwest produced a south-propagating orogen, with the Kalgoorlie, Gindalbie, and Kurnalpi Terranes trapped between in a tectonic-escape corridor. Tectonic escape to the south between bounding strike-slip faults produced back-stepping of facies tracts that simulated basin lengthening, whereas forward-stepping of facies tracts was the response to south-propagating uplift.

Late Archaean (2715–2704 Ma) calc-alkaline volcanic complexes in the Kurnalpi Terrane are identical in facies and geochemistry to modern intra-arc volcanic complexes. Preserved volcanic rocks and associated feldspathic sedimentary rocks represent proximal to medial submarine facies of submarine to locally emergent intra-oceanic arc-related volcanoes. The least-altered volcanic rocks are dominantly andesite but range from basalt and basaltic andesite to rare rhyolite, and are the product of magmas similar in composition to those of modern arcs. Intermediate magmas were most likely derived from large ion lithophile element (LILE) enriched mafic magmas by fractional crystallisation (with or without assimilation) processes. The Kurnalpi Terrane thus provides an example of a Late Archaean volcanic arc in which hydrated mantle wedge melting was the main mechanism for magma genesis. TTD-suite volcanism derived from slab melting was either absent or played a subordinate role. The adjacent Gindalbie Terrane contains younger (∼2692–2680 Ma) bimodal (basalt–rhyolite) volcanic complexes, with associated quartz-rich sedimentary rocks, and calc-alkaline intermediate-silicic volcanic complexes. Volcanosedimentary basement to the Gindalbie volcanic sequences is deeply eroded equivalents of the calc-alkaline volcanic complexes, their associated sedimentary rocks and younger basaltic sequences found in the Kurnalpi Terrane. Gindalbie basalt–rhyolite successions locally contain volcanic-hosted massive Cu–Zn mineral deposits. Rhyolites derived by low-pressure fractional crystallisation, or melting, of andesites are more abundant than in the Kurnalpi volcanic complexes. Facies associations and the local occurrence of distinctive incompatible element-enriched, mildly peralkaline (A-type) rhyolites are consistent with rifting of a mature arc system. The two terranes most likely represent volcanic evolution of the same Late Archaean volcanic arc but are different tectonic fragments that were welded together by ∼2660 Ma.

The Penny Dam, Belches, Yilgangi, White Hills, Granny, Royal, Lucky, Brock and Wallaby Supersequences of the Kurnalpi Terrane crop out in synclines that are the erosional remnants of basins that developed as linear zones of subsidence between approximately north-trending compartment-bounding faults. Dominant sedimentary facies range from gravel-rich and sand-rich concentrated density-flow deposits to thickly and thinly bedded Bouma-type turbidites. Background deposits are black shales or laminated green mudstones, and banded iron formation is preserved in some condensed sections. Periods of non-deposition are recorded by bedded chert, which is the product of early diagenetic sea-floor silicification. The basins were separate deep-marine canyon to linear-fan systems that were linked laterally and distally by mud-rich deposits. There is only minor evidence for fault-anchored, canyon-margin slope aprons. Basin development occurred during two stages separated by a period of deformation, uplift and erosion. Sparse palaeocurrents establish sediment dispersal was to the south or southeast, indicating that uplift to the north or northwest controlled palaeoslopes. Stacking of lithofacies is aggradational, and consistent with deposition in fault-bound basins. Tectonostratigraphic equivalence with siliciclastic supersequences of the Kalgoorlie and Gindalbie Terranes is established by common depositional systems, stratigraphic styles and stratigraphic responses to tectonic forcing. Consequently, the siliciclastic supersequences represent overlap (or late-stage) basins that tied together arc-related terranes following terrane amalgamation. Similar depositional facies, aggradational styles of facies stacking and two-stage development characterise the syncollisional Plio-Pleistocene Coastal Range Basin of Taiwan. Modern analogues are the deep-marine Southern Longitudinal and Taitung Troughs off southeastern Taiwan that are being filled by synorogenic sediments derived from the Taiwan Orogen.

Reassessment of Late Archaean tectonostratigraphic architecture of the Eastern Goldfields Superterrane is based on 35 new SHRIMP U-Pb zircon ages of supracrustal sequences. The superterrane comprises at least five terranes with ∼2810 to ≤2657 Ma volcanic and sedimentary rocks amalgamated by ∼2660 Ma. Each terrane has distinctive stratigraphy, volcanic facies, geochemistry and timing of volcanism. The Kalgoorlie Terrane comprises a >2715 to ∼2692 Ma plume-influenced, but deep-marine, mafic-ultramafic succession (Kambalda Sequence) overlain unconformably by a 2686 ± 5 to ≤2666 ± 6 Ma arc-related, deep-marine felsic volcaniclastic-shale succession of tonalite-trondjemite-diorite (TTD) affinity (Kalgoorlie Sequence). Felsic volcaniclastic rocks of the Agnew Domain and northern Yandal Belt are included in the Kalgoorlie Terrane, based on their similar age and geochemistry. The terrane also contains enclaves of >2740 Ma volcanic sequences that are remnants of autochthonous basement to the Kambalda Sequence. Arc-related bimodal and intermediate volcanic rocks of the Gindalbie Terrane, ranging in age from 2693 ± 4 to 2676 ± 5 Ma, are coeval with but geochemically distinct from the Kalgoorlie Sequence. They overlie sequences similar in age and composition to volcanic rocks of the Kurnalpi Terrane. The Kurnalpi Terrane comprises deep-marine, calc-alkalic mafic and intermediate volcanic rocks (Kurnalpi Sequence) ranging in age from 2715 ± 5 to 2704 ± 4 Ma, overlain conformably by mafic to ultramafic lavas (Minerie Sequence). Although of overlapping age, arc-related rocks in the Kambalda and Kurnalpi-Minerie Sequences are geochemically different. SHRIMP dating has identified older volcanic sequences in the Laverton (≤2808 ± 8 Ma) and Duketon-Burtville (2805 ± 5 Ma) Terranes, with komatiite-hosted Ni-sulphide deposits at Windarra, in the Laverton Sequence, linked to mafic-ultramafic magmatism ∼100 million years older than in the Kalgoorlie Terrane. Older sequences in the Laverton Terrane are autochthonous basement to the Kurnalpi Sequence. Synorogenic siliciclastic sequences occur as erosional remnants either in synclinal structures or adjacent to terrane-scale faults, and overlie a regional-scale unconformity. Detrital zircon ages indicate deposition after 2657 ± 4 Ma, placing important age constraints on the principal shortening event (D2) and peak metamorphism. Detrital zircon ages also indicate older sources at ∼2730, ∼2800, ∼2950, ∼3000 Ma and, less commonly, >3400 Ma. Many zircon age-populations correspond to known supracrustal and crustal rocks in the Yilgarn Craton, but some have no known source in the Eastern Goldfields Superterrane. Superterrane-wide distribution and evidence for erosion of all crustal and supracrustal rocks ≥2660 Ma in age requires deposition of these sequences after terrane amalgamation, most likely synorogenic to collision between the Eastern Goldfields Superterrane and the Yilgarn Craton.

Albion Downs is a structural domain within the Agnew-Wiluna Greenstone Belt of Western Australia, which contains one of the most highly Ni-endowed komatiite sequences in the world. Albion Downs comprises adcumulate-textured pods and lenses, which are flanked by thinner meso- and orthocumulate-textured units. Basal massive nickel-sulphide mineralisation (e.g. Jericho) generally occurs in the thinner meso- and orthocumulate-textured units, whereas stratabound disseminated nickel-sulphide mineralisation (e.g. Jordan) is hosted in the largest adcumulate-textured pod. After reaching sulphide-saturation, basal massive sulphides formed in settings where magma flow was less fast and turbulent than in channels. Conversely, in channellike settings sulphide blebs were entrained in the flow, thus forming disseminated sulphides. Platinum-group element lithogeochemistry indicates that the signature associated with the oreforming process is only recorded

The Mount Keith (MKD5) nickel sulfide deposit is one of the largest komatiite-hosted nickel sulfide deposits in the world; it is hosted by a distinctive spinifex-free, cumulate-rich, ultramafic horizon/unit termed the Mount Keith Ultramafic (MKU). The Mount Keith Ultramafic shows significant variation along its lateral extent. The internal architecture is made up of adcumulate-textured pods and lenses, which are flanked by thinner meso- and orthocumulate-textured units, overlain by pyroxenitic and gabbroic horizons. The lateral and vertical changes in the geometry and internal architecture reflect variations in the lithological association and emplacement conditions along the strike extent of the belt. The chilled margins of the Mount Keith Ultramafic unit contain ∼1,200 ppm Ni. Olivine cumulates average ∼2,500–3,500 ppm Ni, with few exceptions (Ni > 4,500 ppm) reflecting occurrence of minor nickel sulfides, whereas pyroxenites and gabbros generally contain, respectively, ∼1,500–2,000 and ∼100–1,000 ppm Ni. Olivine cumulates generally contain low Cr concentrations ( 5,000 ppm Cr). The internal stratigraphy of the Mount Keith Ultramafic unit may be subdivided into two groups based on rare earth element distribution. The chilled margins and the internal units of the Main Adcumulate domain display LREE-enriched patterns [(La/Sm)n > 1–3] and negative Eu, Hf, Zr, Nb, and Ti anomalies. The internal units in the Western Mineralized Zone generally display flat chondrite-normalized REE patterns and only minor negative Nb anomalies. The pattern of platinum-group element (PGE) distribution varies greatly along the strike extent of the Mount Keith Ultramafic unit. The chilled margins display relatively low absolute concentrations [PGE (excl. Os) ∼16 ppb] and relatively fractionated patterns, with subchondritic Pt/Pd ratios (∼1.5), and superchondritic Pd/Ir ratios (∼3). The PGE trends in the thick adcumulate-textured pods containing widespread nickel sulfide mineralization display positive correlation with sulfide abundance, whereas fractionated pyroxenites and gabbros in the thinner domains display highly depleted PGE concentrations and generally show compatible PGE trends. The nickel sulfide ore typology and style vary greatly along the strike extension of the Mount Keith Ultramafic unit. Basal massive nickel sulfide mineralization (e.g., Sarah’s Find) occurs in the thinner meso- and orthocumulate-textured units, whereas stratabound disseminated nickel sulfide mineralization (e.g., MKD5 Ni Deposit) is hosted in the adcumulate-textured pods. We hypothesize that the very low PGE content of the initial liquid of the Mount Keith Ultramafic unit indicates that the initial magma pulse that penetrated through the dacite host-rock had already equilibrated with sulfides at depth and/or carried entrained immiscible sulfide blebs. We argue that upon emplacement, the intruding magma experienced a significant thermal shock at the contact with water-saturated volcaniclastic breccias. The sudden chilling would have increased the viscosity of the magma, possibly to the point where it was no longer able to sustain the suspension of the immiscible sulfide liquid. As a result, the sulfide blebs coalesced and formed the basal massive sulfide nickel sulfide mineralization at the base of the sill (i.e., Sarah’s Find). Prolonged focused high volume magma flow within the sill resulted in the emplacement of a thick, lens-shaped accumulation of olivine adcumulate. Local variations in intensive parameters other than crustal assimilation (e.g., T, fO2, fS2) may be principally responsible for sulfide supersaturation and controlled the local distribution of stratabound disseminated nickel sulfide mineralization (e.g., MKD5 Ni Deposit), generally localized within the core of the thicker dunite lenses.

The Mt Tom Price deposit is a world-class high-grade hematite deposit in the Hamersley Province of Western Australia with an original resource of 900 Mt of almost pure hematite, averaging 63·9 wt-%Fe. Petrological and geochemical studies at both the Southern Ridge and the North deposit at Mt Tom Price have identified three hypogene alteration zones between unmineralised banded iron formation (BIF) and high-grade iron ore: distal magnetite-siderite-stilpnomelane; intermediate hematite-magnetite-ankerite-talc-chlorite; and proximal martite-microplaty hematite-magnetite-apatite alteration zones. Fluid inclusions trapped in siderite within the distal magnetite-siderite-stilpnomelane alteration zone at the North deposit revealed primary high salinity (25·5 eq.wt-%NaCl–CaCl2) inclusions that homogenised between 107 and 142°C into liquid. Fluid inclusions trapped in ankerite within ankerite-microplaty hematite veins in the intermediate hematite-ankerite-magnetite-talc-chlorite alteration zone at the Nort...

Two main deformational phases are recognised in the Archaean Boorara Domain of the Kalgoorlie Terrane, Eastern Goldfields Superterrane, Yilgarn Craton, Western Australia, primarily involving south-over-north thrust faulting that repeated and thickened the stratigraphy, followed by east-northeast – west-southwest shortening that resulted in macroscale folding of the greenstone lithologies. The domain preserves mid-greenschist facies metamorphic grade, with an increase to lower amphibolite metamorphic grade towards the north of the region. As a result of the deformation and metamorphism, individual stratigraphic horizons are difficult to trace continuously throughout the entire domain. Volcanological and sedimentological textures and structures, primary lithological contacts, petrography and geochemistry have been used to correlate lithofacies between fault-bounded structural blocks. The correlated stratigraphic sequence for the Boorara Domain comprises quartzo-feldspathic turbidite packages, overlain by hi...

The Quadrilatero Ferrifero has some of the largest iron and gold deposits in the world and is a major geotectonic unit of the Sao Francisco Craton in Brazil. U–Pb zircon SHRIMP geochronology of six detrital sedimentary and metasedimentary rocks (114 zircon crystals, 118 spot analyses) has improved the understanding of the sedimentary processes and provenance ages of both rocks and the associated iron formation. The age of deposition of the iron formation is constrained between 2.58 and 2.42 Ga. The presence of an old Paleoarchean crust is dated in detrital zircon crystals, including the oldest zircon in South America (3809±3 Ma). Only high-Th/U, magmatic zircon crystals are present in the dated sedimentary rocks, and these indicate that the crust of the region was formed mostly during the Jequie cycle (six age peaks between 3055 and 2635 Ma). This time span of ∼420 m.y. is similar to the duration of a long-lived Wilson cycle. Most of the Rio das Velhas Basin was filled during approximately 30 m.y. between 2746 and 2717 Ma, though volcanism probably started earlier. The youngest detrital zircon age from the Minas Supergroup indicates that the intracratonic basin fill, including the iron formation, was deposited after 2580 Ma. Therefore, the crust was cratonized shortly after the intrusion of minor granitic bodies at around 2.62–2.58 Ga. A large gap in orogenic activity is indicated by the absence of zircon ages of 2580–2182 Ma.

Analysis of the tectonostratigraphic records of Late Archean to Early Paleoproterozoic terranes indicates linkage between global tectonics, changing sea levels and environmental conditions. A Late Archean tectonic cycle started at ~2.78 Ga involving the breakup of a pre-existing continent (Vaalbara) and the most prodigious period of generation and preservation of juvenile continental crust recorded in Earth history during a period of plume breakout (~2.72 to 2.65 Ga) accompanied by high sea levels. During this period, cratons formed by accretion of granitoid‐greenstone terranes at convergent margins started to aggregate into larger continents (e.g. Kenorland). Lower sea levels between ~2.65 and 2.55 Ga were followed by a second (~2.51 to 2.45 Ga) period of plume breakout resulting in a global peak in magmatism, high sea levels and deposition of banded iron formations (BIF) on the trailing margins of the Pilbara and Kaapvaal cratons. Cratons in South Australia, Antarctica, India, and China record convergent margin magmatism, orogeny and high-grade metamorphism between 2.56 and 2.42 Ga. Continued aggregation of continental fragments (e.g. amalgamation of Indian cratons) may have formed the Earth’s first supercontinent by ~2.4 Ga with a return to low sea levels and relative tectonic quiescence before the supercontinent started to breakup from ~2.32 Ga.

High-grade iron mineralisation (>65%Fe) in the North Deposit occurs as an E-W trending synclinal sheet within banded iron formation (BIF) of the Early Proterozoic Dales Gorge Member and consists of martite-microplaty hematite ore. Three hypogene alteration zones between unmineralised BIF and high-grade iron ore are observed: (1) distal magnetite-siderite-iron silicate, (2) intermediate hematite-ankerite-magnetite, and (3) proximal martite-microplaty hematite-apatite alteration zones. Fluid inclusions trapped in ankerite within ankerite-hematite veins in the hematite-ankerite-magnetite alteration zone revealed mostly H2O–CaCl2 pseudosecondary and secondary inclusions with salinities of 23.9±1.5 (1σ, n=38) and 24.4±1.5 (1σ, n=66) eq.wt.% CaCl2, respectively. Pseudosecondary inclusions homogenised at 253±59.9°C (1σ, n=34) and secondary inclusions at 117±10.0°C (1σ, n=66). The decrepitation of pseudosecondary inclusions above 350°C suggests that their trapping temperatures are likely to be higher (i.e. 400°C). Hypogene siderite and ankerite from magnetite-siderite-iron silicate and hematite-ankerite-magnetite alteration zones have similar oxygen isotope compositions, but increasingly enriched carbon isotopes from magnetite-siderite-iron silicate alteration (−8.8±0.7‰, 1σ, n=17) to hematite-ankerite-magnetite alteration zones (−4.9±2.2‰, 1σ, n=17) when compared to the dolomite in the Wittenoom Formation (0.9±0.7‰, 1σ, n=15) that underlies the deposit. A two-stage hydrothermal-supergene model is proposed for the formation of the North Deposit. Early 1a hypogene alteration involved the upward movement of hydrothermal, CaCl2-rich brines (150–250°C), likely from the carbonate-rich Wittenoom Formation (δ13C signature of 0.9±0.7‰, 1σ, n=15), within large-scale folds of the Dales Gorge Member. Fluid rock reactions transformed unmineralised BIF to magnetite siderite-iron silicate BIF, with subsequent desilicification of the chert bands. Stage 1b hypogene alteration is characterised by an increase in temperature (possibly to 400°C), depleted δ13C signature of −4.9±2.2‰ (1σ, n=17), and the formation of hematite-ankerite-magnetite alteration and finally the crystallisation of microplaty hematite. Late Stage 1c hypogene alteration involved the interaction of low temperature (~120°C) basinal brines with the hematite-ankerite-magnetite hydrothermal assemblage leaving a porous martite-microplaty hematite-apatite mineral assemblage. Stage 2 supergene enrichment in the Tertiary resulted in the removal of residual ankerite and apatite and the weathering of the shale bands to clay.

Sedimentary rocks in S macrobands of the Dales Gorge Member are the key to identifying the depositional setting of banded iron formation, because they can be described and interpreted by analogy to modern marine sediments. S macrobands comprise mostly shelf-derived epiclastic and volcaniclastic mud-rich turbidites, carbonate-rich turbidites and hemipelagites. Ash-fall tuffs occur in S macrobands and in their BIF equivalents, but are not diagnostic of the depositional setting other than it being below wave base and coeval with distant volcanism. Sedimentological content and stratigraphic geometry define the sedimentary rocks in S macrobands as being the deposits of distal lowstand fans in a sediment-starved basin-plain setting. Sedimentation was pulsed, with gaps between sedimentation units being recorded by province-scale seafloor silicification that produced bedded chert. BIF occurs in some S macrobands, but sedimentary rocks characteristic of S macrobands do not occur in BIF macrobands. Mudrock-chert couplets in S macrobands are remarkably similar in internal structure, areal extent and thickness to BIF-chert couplets in BIF macrobands, suggesting that the precursor sediments to BIF were also deposited from episodic density currents. In contrast to the shelf source of sedimentary rocks in S macrobands, the precursor sediments to BIF were probably iron-rich granular muds derived from the flanks of submarine volcanoes, and brought to the depositional site by bottom currents. Basin filling therefore reflects competitive deposition between shelf-derived and intrabasinally derived sediments. Sedimentation units capped by bedded chert in S and BIF macrobands may record depositional rhythms at the scale of Milankovitch Cycles, whereas depositional sequences are composed of an underlying S macroband and an overlying BIF macroband.

Eleven high precision (±2–5 million years) SHRIMP zircon U–Pb ages have been obtained from felsic rocks within a single stratigraphic section of late Archaean volcanic and sedimentary rocks in the east Pilbara of Western Australia. The stratigraphic succession (Nullagine and Mount Jope Supersequences in sequence-stratigraphic terminology, Fortescue Group in lithostratigraphic terminology) is interpreted to be the rock record of three major geotectonic cycles that formed in an extensional, rift-related environment between about 2772 and 2715 Ma. The geochronology is constrained by a detailed stratigraphic framework based on unconformities and supported by a preliminary magnetostratigraphy. Field mapping, geochemical and petrographic studies have shown that previously unrecognised thin felsic tuff bands are interbedded in subaerial flood basalt piles and mafic tuffs. While flood basalts and proximal felsic volcanic rocks comprise by volume most of the volcanogenic components of the succession, felsic volcanism is now known to have been active periodically through each geotectonic cycle. The succession covers a time period of about 57 million years. The lower ∼1400 m of a thick (∼1700 m) clastic sedimentary succession from the oldest geotectonic cycle was deposited at a rate of about 100 m per million years over a mean time period of 14 million years. In contrast, a younger ∼150 m thick cogenetic tuff-basalt unit accumulated in less than 3 million years, and others probably accumulated at similar rates, comparable to those of Phanerozoic flood basalts. Unconformities in the succession are shown to be of variable duration and one unconformity marking the boundary between the first and second geotectonic cycles may represent a time-gap of more than 10 million years. The unconformity-based stratigraphic framework, the new geochronology and palaeomagnetic studies [J. Geophys. Res. 108 (2003) B12, 2551, EMP 2-1 to 2-21] have been combined to determine a possible late Archaean continental drift rate for one part of the succession, implying a period of motion as fast as or up to five times faster than any known from the Phanerozoic.

The paper investigates the role of primary magmatic phases in the fractionation and concentration of PGE in Archaean mafic and ultramafic systems. The composition of chromites and olivines in sulphur-poor (S 200 ppb) reflect the presence of PGM. Chromites from Fred’s Flow komatiitic basalt contain Ir-rich clusters, whereas Pt enrichments (>370 ppb) in Boston Creek ferropicritic basalt reflect the presence of Pt-rich compounds. The presence of PGE-bearing alloys in Theo’s Flow and Fred’s Flow is due to late S-supersaturation, whereas the presence of Pt-rich compounds in Boston Creek Flow reflects high state of melt oxidisation. The lack of PGE-bearing alloys in the olivines and chromites of komatiites can be explained by thermal instability of PGM, depletion in PGE at the mantle source, early S-supersaturation, the oxidisation conditions of the melt, or a combination of these factors.

The Kanowna Belle Gold Mine is a Late Archaean orogenic lode-gold deposit hosted by felsic volcaniclastic and intrusive rocks (porphyries) of the Kalgoorlie Terrane, Western Australia. Rare gold occurs in fragments of veins and alteration that form clasts within the Black Flag Group volcaniclastic rocks at the Kanowna Belle mine, indicating that epithermal gold mineralisation accompanied Black Flag Group volcanism. The SHRIMP U–Pb zircon age of the volcaniclastic unit is 2668±9 Ma, and xenocrystic zircons with ∼2.68, 2.70 and 2.71 Ga age groupings are common. The Black Flag Group rocks are faulted by a D1 thrust, and ∼2670 Ma is thus an older limit for regional D1 deformation. Although SHRIMP U–Pb zircon ages of felsic porphyries commonly give the best constraints on the timing of deformation and structurally controlled gold mineralisation, the data are complex and dates from single samples can be ambiguous. Four Porphyry samples from the Kanowna Belle Gold Mine were analysed. Backscattered electron and cathodoluminescence imaging show that most magmatic zircon in the porphyries is either high-U and metamict, or restricted to rims on older xenocrysts that are too narrow to be dated by SHRIMP. Some porphyries appear to have been saturated with zircon at source and contain only xenocrystic zircons. Zircons that are interpreted to be magmatic in a sample of the mineralised Kanowna Belle Porphyry gives a mean age of 2655±6 Ma. The Kanowna Belle Porphyry is cross cut by regional D2 fabrics and ∼2655 Ma is thus the maximum age for regional D2 deformation. This is a maximum age for epigenetic lode-gold mineralisation. The age of resetting of high-U zircon grains (2.63 Ga) and the age of ore-related Pb–Pb galenas (2.63 Ga) serves as an approximate date for lode-gold mineralisation. If the complex zircon history of the felsic porphyries at Kanowna Belle is typical of this suite throughout the Eastern Goldfields Province, it is clear that existing single zircon dates from this Province require reevaluation, backed up by careful backscattered and cathodoluminescence imaging and textural studies.

The Early Palaeoproterozoic Brockman Supersequence comprises banded iron formation (BIF), bedded chert, limestone, mudrock, sandstone, breccia, tuffaceous mudstone, ashfall tuff and, in sections not reported here, basalt and rhyolite. Density current rhythms are preserved in sandstones, mudrocks, tuffaceous mudstones and limestones. Relics of similar rhythms in BIF imply that its precursor sediments were also deposited by density currents. Hemipelagic deposits are siliciclastic or mixed siliciclastic–volcaniclastic mudstones. Bedded chert, chert nodules and the chert matrix of BIF preserve evidence for formation by diagenetic replacement. For bedded chert (and chert nodules), silica replacement occurred before compaction close to or at the sediment–water interface, indicating that it is siliceous hardground. The chert matrix of BIF formed during compaction but before burial metamorphism. Original sediments were resedimented from two sources: (1) limestone, mudrock, sandstone, breccia and tuffaceous mudstone from a shelf; and (2) BIF from within the basin realm. Shelf sediments were resedimented to basin-floor fans during third-order lowstands. The precursor sediments to BIF are interpreted to have been granular hydrothermal muds, composed of iron-rich smectite and particles of iron oxyhydroxide and siderite that were deposited on the flanks of submarine volcanoes and resedimented by density currents. Resedimentation occurred by either bottom currents or gravity-driven turbidity currents, and the resulting sediment bodies may have been contourite drifts. The concept that BIF records high-frequency alternating precipitation from ambient sea water of iron minerals and silica is negated by this study. Instead, it is postulated that the precursor sediments to BIF originated in much the same way as modern Red Sea hydrothermal iron oxide deposits, implying that at least the particles of iron oxyhydroxide originated from the oxidation of vent fluids by sea water. Several orders of cyclicity in basin filling establish a relationship between rising to high sea levels, episodic sea-floor hydrothermal activity and BIF that is reminiscent of the link between eustacy and spreading-ridge pulses.

The Carajas iron ore deposits in the eastern part of the Amazonas Craton contain approximately 18 000 Mt of hematite ore with > 66%Fe. These deposits are hosted by jaspilitic banded iron formation (BIF) of the Carajas Formation which together with metavolcanic rocks comprise the ~2·8 Ga Grao Para Group of the Itacaiunas Supergroup in the ~1000 km long by 100 km wide, eastwest trending Carajas Synclinorium. The Carajas Formation comprises discontinuous layers and lenses of partly dolomitised jaspilitic BIF (17-43%Fe and 35-61%SiO2), bodies of jaspilitic BIF and lenses of high-grade iron ore, cut by mafic sills and dykes. Dolomitisation of the BIF occurs mainly at the base of the Carajas Formation. With increasing amounts of dolomite, the BIF lamination (microbanding) and other fine primary structures are progressively obliterated resulting in irregular alternating carbonate and iron-oxide mesobands. The high-grade iron ores occur as tabular bodies of soft friable hematite with smaller lenses of har...

Porphyritic and peraluminous granitoids of the Lesser Himalayan granite belt fringe the High Himalaya from Nepal to Pakistan. Magmatic zircons in the Chor granitoid in Himchal Pradesh define a SHRIMP U–Pb age of 823±5 Ma. This Neoproterozoic age contrasts with Cambro-Ordovician ages for other dated Lesser Himalayan granites, but is coeval with granite magmatism in the South China craton. Neoproterozoic magmatism within the northern margin of Gondwanaland may provide a more local source for detrital zircons in High Himalayan metasediments during the Neoproterozoic and early Paleozoic than the recently postulated East African orogen.

The Early Archean Bamboo Creek gold deposit contrasts with most other orogenic deposits because of its relatively early timing in the tectonic evolution of the Pilbara granitoid-greenstone terrane. The Bamboo Creek deposit is situated in a bedding-parallel, brittle-ductile shear zone (the Bamboo Creek shear zone) within a komatiite sequence. The laminated quartz-carbonate gold lodes occur in carbonate-altered boudins within the Bamboo Creek shear zone and are associated with early sinistral, northeast-up deformation in the shear zone, whereas dextral reactivation of the zone postdates gold deposition. Gold-related alteration zones reflect an increase in X CO 2 toward the mineralized zone. Variations in original host-rock composition give rise to asymmetric alteration zoning, with a fuchsite-carbonate zone in the more Mg- and Cr-rich cumulate-textured footwall and a chlorite-quartz zone in the more aluminous spinifex-textured hanging wall. The alteration envelope is enriched in Na 2 O, K 2 O, Rb, Pb, As, and Sb. Whereas pyrite and minor chalcopyrite occur in all alteration zones, tetrahedrite, galena, and sphalerite are strongly associated with gold in the lodes. The alteration and metal enrichment of the Bamboo Creek gold deposit are indistinguishable from those of other orogenic (mesothermal) lode gold deposits in Archean terranes. Carbonate δ 13 C (PDB) and δ 18 O (SMOW) isotope signatures are consistent throughout the alteration envelope at 0.2 ± 0.6 and 14.6 ± 0.6 per mil, respectively. The δ 13 C value, in particular, is higher than typical values for orogenic gold deposits, implying interaction of auriferous fluids with preexisting marine carbonates that formed during an early sea-floor alteration event. The temperature of deposition, estimated from chlorite thermometry and alteration assemblages, is about 250°C, which is within the lower part of the range for orogenic gold deposits. Lead-lead model ages for galena, together with the relationships between the Bamboo Creek shear zone and dated granites, indicate a relatively early age of gold deposition of ca. 3400 Ma. Correlation of structures associated with gold deposition and regional structural phases shows that gold deposition was most likely related to an extensional tectonic phase. The early timing and association with extension is unlike the tectonic setting of other Archean gold deposits, which tend to form during the final, compressional or strike-slip stages of orogenesis. The Bamboo Creek gold mineralization may have been related to an Early Archean lower crustal delamination event. This may explain the anomalous timing and the low gold endowment of the Pilbara relative to Late Archean greenstones.

The Melita Volcanic Complex is a Late Archaean bimodal rhyolite/basalt volcanic succession within the Gindalbie Terrane in the Eastern Goldfields Province of the Yilgarn Craton. The Melita Complex has been dated by ion probe at 2683±3 Ma (95%) and forms part of a distinctive 2681–2692-Ma volcanic association that records bimodal (basalt/rhyolite) and calc–alkaline intermediate-silicic volcanism at several discrete volcanic centres, and which locally hosts volcanic massive sulphide mineralisation (Teutonic Bore). Approximately 3 km of stratigraphic thickness is exposed in the Melita area. The upper 1–1.5 km of the exposed succession is dominated by subaqueously resedimented volcaniclastic sandstones and breccias, rhyolite flows and sills. Primary subaerial pyroclastic deposits including ignimbrites have not been identified in this study, although subaerial explosive activity is indicated by the occurrence of accretionary lapilli and the abundance of vitric material (shards) and pumice fragments in resedimented deposits. The lower part of the succession is dominated by pillowed to massive basalt lavas, and in situ and resedimented mafic hyaloclastites. Mafic extrusive and intrusive rocks are tholeiitic with trace element concentrations similar to modern arc tholeiites. Felsic volcanic rocks at Melita are dacite to high-silica rhyolite. They are highly enriched in incompatible elements (particularly high field strength element-enriched), compared to other felsic associations in the Eastern Goldfields Province, representing evolved partial melts of heterogeneous intermediate arc-type crust. The volcanic facies and geochemistry of volcanic rocks at Melita are consistent with those observed in modern intra-arc or arc-rift settings, and the succession is interpreted to represent the initial stages of back-arc rifting within a complex convergent margin.

Rocks from the Sulphur Springs Group, a newly identified stratigraphic succession hosting volcanogenic massive sulphide (VMS) base-metal deposits in the Soanesville Belt, Pilbara Craton, northwestern Australia, have been analyzed by sensitive high-resolution ion microprobe (SHRIMP) U–Pb zircon mass-spectrometry to determine their age and tectonostratigraphic relationships. Most volcanism occurred between 3238 and 3235 Ma, distinctly different from the time interval spanned by the Wyman Formation (type section is 3315 Ma, other dates ∼3325 Ma) with which it was previously correlated. Outlying volcanic rocks with similar geochemistry at the Bernts and Obelix prospects also produce dates from 3240 to 3235 Ma and are, therefore, best interpreted as structurally-detached fragments of the Sulphur Springs Group. The Strelley Granite, an intrusion which shares geochemical characteristics with the overlying volcanic rocks, also yields similar ages, thus extending the period of temporally-linked extrusive–intrusive silicic magmatism in the evolution of the Pilbara Craton. Model Pb–Pb dating of galena from the Zn–Cu mineralization at the various VMS prospects has yielded ages consistent with the zircon U–Pb ages of the host rocks, indicating that the hydrothermal mineralizing systems were contemporaneous with and apparently initiated by igneous activity. An epicontinental tectonic setting for the Sulphur Springs Group during VMS mineralization is implied by the broad range of old zircon ages obtained from a tuff at the base of the volcanic pile. As the igneous episode coincides with the peak regional metamorphic event recorded in other east Pilbara supracrustal rocks and with voluminous intrusive activity in nearby granitoid complexes, it marks a major event in the crustal evolution of the eastern Pilbara Craton.

Background Major Trauma Care is complex and requires robust communication systems between multidisciplinary teams. At Nottingham University Hospitals, major trauma patients requiring emergency surgery are prioritised in theatres creating competition for resources. This requires the Theatre Coordinator receiving appropriate patient information from the Emergency Department to determine the surgical urgency. We aimed to evaluate the existing theatre booking process for major trauma patients, identify key problems in practice, and redesign and test any new system prior to implementation. Methodology A literature review, analysis of existing major trauma care activity and historical local incident reports helped identify potential or actual system problems. Fieldwork enabled observation of the booking process in practice. A questionnaire and focus groups were used to explore existing practices and inform any redesign by consensus amongst an expert panel. Testing this new tool was initiated using simple desktop based simulation exercises. Results The literature and local data described clear consequences of failure to provide adequate patient information in a time critical manner. An existing major trauma theatre booking form was found to be used infrequently and inconsistently, with Co-ordinators favouring a more familiar generic form. Questionnaire data and focus groups with theatre staff, surgeons and anaesthetists (n = 84) distinguished critical versus surplus information for theatre planning, enabling redesign of the form, structured using key information in a chronological systematic manner. Next Steps The new form is now being tested using desktop simulations based on real cases with theatre coordinators, comparing useability and accuracy of data transmission with the generic form. This will guide further modifications before trialling it in practice. Further steps anticipated include production of a standardised handover proforma to be implemented in the Emergency Department, and evaluation of whether the final theatre booking form also provides a team briefing tool for when the patient arrives in theatres. References Flin R, O’Connor P, Chrichton M. Safety at the Sharp End. A guide to non-technical skills . Burlington: Ashgate Publications; 2012 Leonard M, Graham S, Bonacum D. The human factor: the critical importance of effective teamwork in providing safe care. Qual Saf Healthcare 2004;13, 85–90 Barach P, Weinger MB. Trauma team performance. Wilson WC, Grande CM, Editors: TRAUMA : Resuscitation, Anesthesia and Emergency Surgery. Chapter 6. Taylor and Francis: NewYork, pp. 101–13, 2007 MCCulloch, Rathbone, & Catchpole, 2011. Inteventions to improve teamwork and communications among healthcare. British Journal of Surgery , 98, 469–479

U–Pb (SHRIMP) detrital zircon age patterns are reported for 12 samples of Permian to Cretaceous turbiditic quartzo‐feldspathic sandstone from the Torlesse and Waipapa suspect terranes of New Zealand. Their major Permian to Triassic, and minor Early Palaeozoic and Mesoproterozoic, age components indicate that most sediment was probably derived from the Carboniferous to Triassic New England Orogen in northeastern Australia. Rapid deposition of voluminous Torlesse/Waipapa turbidite fans during the Late Permian to Late Triassic appears to have been directly linked to uplift and exhumation of the magmatically active orogen during the 265–230 Ma Hunter‐Bowen event. This period of cordilleran‐type orogeny allowed transport of large volumes of quartzo‐feldspathic sediment across the convergent Gondwanaland margin. Post‐Triassic depocentres also received (recycled?) sediment from the relict orogen as well as from Jurassic and Cretaceous volcanic provinces now offshore from southern Queensland and northern New Sout...

Greenstone belts in the northern Murchison Terrane of the Yilgarn Craton contain an extensive suite of 2.9–3.0 Ga, porphyritic komatiites and komatiitic volcaniclastic rocks. These unusual Ti-rich Al-depleted komatiites have been sampled at Gabanintha and are characterised by higher incompatible-element abundances than most suites of Barberton-type Al-depleted komatiites. They form a petrogenetically related group with similar Ti- and incompatible-element-rich, Al-depleted porphyritic komatiites and komatiitic volcaniclastic rocks from Karasjok in Norway, Dachine in French Guiana and Steep Rock – Lumby Lake in Canada (here called Karasjok-type komatiites). Their Al-depletion results from magma generation at depths of >250 km in the presence of residual majorite-garnet. The porphyritic textures and abundance of amygdales and volcaniclastic rocks typical of this type of komatiite are features of hydrous ultramafic magmas. The incompatible-element-rich ultramafic rocks from Dachine contain diamonds that were most likely picked up as parent magmas interacted with mantle lithosphere that had been hydrated and chemically modified. Consequently the interaction of Karasjok-type komatiite magmas with thick, island arc or continental mantle lithosphere may have resulted in their elevated water and incompatible-element contents. The occurrence of Karasjok-type komatiite lavas and volcaniclastic rocks in the northern Murchison Terrane suggests that during the Late Archaean that terrane had a hydrated, metasomatised or subduction-modified mantle lithosphere.

The bimodal volcanic and coarse siliciclastic sedimentary rocks of the Koras Group are virtually undeformed and weakly metamorphosed, and overlie the highly metamorphosed and strongly deformed rocks of the Kheis subprovince of the Namaqua—Natal Metamorphic Province with a sharp erosional unconformity. Zircons from the Swartkopsleegte quartz porphyry, close to the base of the Koras Subgroup, have been dated at 1171 ±7 Ma by SHRIMP. This age is in good agreement with, but far more precise than, previously published ages for the Koras Group. The new age defines the onset of bimodal volcanism in the Koras Group and also indicates that the compressional Kibaran Orogeny in the Namaqua—Natal Province ended before or at ~1170 Ma. The main phase of Kibaran deformation, uplift, and erosion in the Namaqualand sector of the orogen took place in the period between the extrusion of the Wilgenhoutsdriflavas at ~1330 Ma and deposition of the Koras Group at 1171 Ma. Younger ages for peak metamorphism and post-tectonic intrusions (1060 to 1030 Ma) in the Namaqua—Natal Province clearly post-date Kibaran compressional tectonics and magmatic activity by more than 100 Maand are related to a subsequent magmatic event in the orogen. The Koras Group in Namaqualand is widely regarded as a typical representative of the ~1105 Ma Umkondo igneous province, a group of volcano—sedimentary successions and igneous bodies which post-date the Kibaran Orogeny in southern Africa. However, extrusion of the Koras lavas predates the Umkondo suite in Zimbabwe and coeval lavas in Botswana andNamibia by 60 Ma.

Giant iron-ore deposits, such as those in the Hamersley Province of northwestern Australia, may contain more than a billion tonnes of almost pure iron oxides and are the world's major source of iron. It is generally accepted that these deposits result from supergene oxidation of host banded iron formation (BIF), accompanied by leaching of silicate and carbonate minerals. New textural evidence however, shows that formation of iron ore at one of those deposits, Mount Tom Price, involved initial high temperature crystallisation of magnetite-siderite-iron silicate assemblages. This was followed by development of hematite- and ferroan dolomite-bearing assemblages with subsequent oxidation of magnetite, leaching of carbonates and silicates and crystallisation of further hematite. Preliminary fluid inclusion studies indicate both low and high salinity aqueous fluids as well as complex salt-rich inclusions with the range of fluid types most likely reflecting interaction of hydrothermal brines with descending meteoric fluids. Initial hematite crystallisation occurred at about 250 °C and high fluid pressures and continued as temperatures decreased. Although the largely hydrothermal origin for mineralisation at Mount Tom Price is in conflict with previously proposed supergene models, it remains consistent with interpretations that the biosphere contained significant oxygen at the time of mineralisation.

New sensitive high resolution ion microprobe zircon U–Pb dating indicates that the eastern Pilbara Craton contains an extensive suite of variably deformed 3325 to 3310 Ma rhyolites, high-level quartz–feldspar porphyries and granitoids. These range in composition from Na-rich trondhjemite (low-K rhyolite) to K-rich monzogranite, with silica-rich (>68%) biotite (±hornblende) bearing porphyritic granodiorites and monzogranites most abundant. Initial volcanism accompanied regional extension at ∼3325 Ma and was followed by intrusion of high-level porphyritic stocks and emplacement of massive to foliated batholithic granitoids at ∼3315 Ma. The compositions of this volcano plutonic suite suggest that the most likely source for parent magmas is older continental crust with tonalite–trondhjemite–granodiorite suite compositions. Crustally-derived silicic volcanic rocks and granitoids have traditionally been considered rare in pre-3.0 Ga granitoid–greenstone terranes. Evidence from the eastern Pilbara indicates that magmatic recycling of continental crust has occurred at least as early as 3.3 Ga.

The Late Archaean records periods of intense magmatism and the development of prodigious metallogenic provinces of Ni, Fe, Cu Zn and Au deposits. In particular, the period 2.74-2.66 Ga represents one of the most widespread episodes of ultrabasic and basic volcanism preserved in the geological record, as well as anomalously widespread granitoid magmatism. Extensive assemblages of this age, which comprise komatiites and komatiitic basalts derived from mantle plumes, together with tholeiites and calc-alkalic volcanic rocks, are preserved on most Late Archaean cratons. Intense submarine volcanism in plume-like environments resulted in rich komatiite-hosted Ni mineralization in continental-margin basins, and Cu Zn sulphide mineralization in extensional volcanic arcs. Peak submarine magmatism was accompanied by marine transgression and thereby flooding of previously exposed continental crust. Elevated hydrothermal activity and widespread su☐ic conditions in submarine basins are reflected by sulphide-rich carbonaceous sedimentary rocks, that contain the organic remains of bacterial communities, and banded iron formations (BIF). A major episode of mesothermal gold mineralization accompanied accretionary tectonics, as metal-and carbon-rich submarine volcanic and sedimentary successions were subducted or incorporated into nascent continental crust by 2.59 Ga. Comparison with Neoproterozoic and Phanerozoic tectonic and metallogenic patterns indicates that the period 2.78-2.59 Ga represents the first half of an ∼ 360 m.y. global tectonic cycle. This period records the breakup of a supercontinent and the opening and closing of marginal basins along long-lived convergent margins of the external ocean to that supercontinent. Enhanced magmatic events between 2.74 and 2.66 Ga were most likely the result of intrabasinal mantle plumes and a subsequent global plume-breakout event. Together, the plume events were responsible for the extreme environmental conditions during the Late Archaean relative to both the preceding and succeeding periods of Earth history. Interactions between mantle plumes and long-lived convergent margins of a Pacific-type ocean were responsible for the prodigious metal inventory of Late Archaean granitoid-greenstone terranes. Extensive convergent-margin and plume magmatism during that period, coupled with episodic periods of low-angle subduction underplating by oceanic lithosphere, may also have been the cause of development of the buoyant, continental mantle lithosphere that is responsible for the preservation of these highly mineralized cratons. It is also likely that the bonanza metallogenic provinces in the Witwatersrand basin and Paleoproterozoic orogens of West Africa and Laurentia-Baltica reflect interactions of mantle plumes with long-lived convergent margins of the external ocean.

New U–Pb detrital zircon ages from Triassic metasandstones of the Torlesse Terrane in New Zealand are compared with 40Ar/39Ar muscovite data and together, reveal four main source components: (i) major, Triassic–Permian (210–270 Myr old) and (ii) minor, Permian–Carboniferous (280–350 Myr old) granitoids (recorded in zircon and muscovite data); (iii) minor, early middle Palaeozoic, metamorphic rocks, recorded mainly by muscovite, 420–460 Myr old, and (iv) minor, Late Precambrian–Cambrian igneous and metamorphic complexes, 480–570 Myr old, recorded by zircon only. There are also Proterozoic zircon ages with no clear grouping (580–1270 Myr). The relative absence of late Palaeozoic (350–420 Myr old) components excludes granitoid terranes in the southern Lachlan Fold Belt (Australia) and its continuation into North Victoria Land (East Antarctica) and Marie Byrd Land (West Antarctica) as a potential source for the Torlesse. The age data are compatible with derivation from granitoid terranes of the northern New England Orogen (and hinterland) in NE Australia. This confirms that the Torlesse Terrane of New Zealand is a suspect terrane, that probably originated at the NE Australian, Permian–Triassic, Gondwanaland margin and then (200–120 Ma) moved 2500 km southwards to its present New Zealand position by the Late Cretaceous (90 Ma). This sense of movement is analogous to that suggested for Palaeozoic Mesozoic terranes at the North American Pacific margin.

The McPhee Dome and Kelly Belt in the eastern Pilbara Craton contain well-preserved, proximal, shallow-marine, dominantly-intermediate, volcanic successions. These have SHRIMP UPb zircon ages of 3430 ± 3 and 3417 ± 9 Ma respectively, which are younger than geochemically similar ∼3.52 and ∼3.47 to 3.45 Ga suites in other eastern Pilbara greenstone belts. Basalts, andesites and dacites from the McPhee Dome are similar in composition to modern arc rocks, whereas dacites and rhyodacites from the Kelly Belt have geochemical characteristics of Archaean tonalite-trondhjemite-granodiorite (TTG) magmas. The geochemistry of the McPhee Dome basalts, basaltic andesites and dacites most likely reflects infracrustal fractional crystallization of a mantle derived magma combined with assimilation of older crust, or a silicic melt. In contrast the Kelly Belt dacites and rhyodacites were most likely derived by melting of subducted mafic crust. The extensional submarine environment of pre-3.4 Ga, dominantly mafic and intermediate volcanism in the eastern Pilbara differs from that of approximately coeval granitoid magmatism. The pre-3.4 Ga granitoids have the major and trace element features of TTG suites and appear to have been emplaced into already thick crust culminating in core complex formation. Available data are most consistent with growth of the eastern Pilbara Craton in convergent tectonic settings, involving pulses of extensional shallow-marine, arc-like volcanism between 3.52 and 3.42 Ga, overlapping with, and/or punctuated by, periods of crustal thickening and the intrusion of complex TTG granitoid batholiths.

Early Archaean, FeZnCu volcanogenic massive sulphide deposits of the Strelley Belt, Pilbara Craton, occur at the top of a volcanic dominated sequence, at the interface of felsic volcanic rocks and siliceous laminites, beneath an unconformity overlain by clastic sedimentary rocks. The structure of the Sulphur Springs and Kangaroo Caves VMS deposits is relatively simple, with the present morphology reflecting original deposition rather than significant structural modification. The rocks have been tilted giving an oblique cross-sectional view of discordant high-angle, deep penetrating faults in the footwall, which splay close to the zones of volcanogenic massive sulphide mineralization. Faults do not extend far into the overlying sedimentary cover, indicating their syn-volcanic and syn-mineralization timing. Both the Sulphur Springs and Kangaroo Caves sulphide deposits are located within elevated grabens in a setting similar to massive sulphide mineralization in modern back-are environments. Mineralization at Sulphur Springs and Kangaroo Caves is located at the edge of the grabens, at the site of intersecting syn-volcanic extensional faults.

Hydrothermal gold mineralization occurs in banded iron formation and amphibolite host rocks, respectively, in the Main Hill and Zakanaka deposits in the northern sector of the Pilgangoora greenstone belt of the Pilbara Craton. The supracrustal sequences of the greenstone belt have been folded into NS trending, megascale isoclinal F2A folds, which have been refolded into open to tight F2B folds. D2 to D3 strike-slip shear zones developed preferentially along the limbs of F2A isoclinal folds and along the granitoid-greenstone belt contact. Gold mineralization is controlled by F2B folds and shear zones were interpreted to have been activated or reactivated during D2B deformation in both deposits. Gold associated hydrothermal alteration comprises zoned quartz-calc silicate veins and pyrrhotite-pyrite at the Zakanaka deposit and quartz-amphibole-biotite±diopside and pyrrhotite-lollingite-arsenopyrite at the Main Hill deposit. Thermobarometric and textural studies indicate that gold mineralization occurred synchronous with the peak of amphibolite-facies metamorphism in both deposits. Lead isotope studies on gold-associated hydrothermal microcline, titanite and pyrrhotite in the Zakanaka deposit yield a PbPb isochron with an age of 2888.2±6.1 Ma for the alteration and, hence, gold mineralization. This age is confirmed by a concordant PbPb age using SHRIMP on hydrothermal titanite from the Zakanaka deposit of 2904 ± 70 Ma. The initial isotopic ratio in the ore system, estimated using the isotopic composition of hydrothermal microcline, is much more primitive than 2888 Ma Pb from accepted growth curves. Lead-isotope modeling using the possible ages of rock formation and metamorphic events in the eastern Pilbara Craton shows that the primitive Pb isotope signature is consistent with the 2888 Ma age of alteration, if the Pb was derived from old crust which underwent an early high-grade depletion event. The age of hydrothermal, gold-associated alteration at Zakanaka indirectly constrains the age of the F2B folding event and the peak of amphibolite-facies metamorphism in the Pilgangoora greenstone belt to ca. 2.89 Ga. The special position of the Pilgangoora greenstone belt in the central Pilbara, permits the interpretation of the age of gold mineralization in the light of the tectonic evolution in both parts of the craton, and indicates that mineralization and the associated structural and metamorphic events post-dated the main magmatic evolution in both the east and the west Pilbara Craton, but coincided with late deformational events along strike-slip shear zones in the west Pilbara and late syn- to post-tectonic granitoids and associated metamorphism in the east Pilbara.

The Pilbara Block provides a record of Archaean continental growth involving the tectonic accretion of outboard island-arcs and collisions with other continental-scale fragments. This record of continental growth is balanced by breakup and strike-slip dismemberment of the continent. New SHRIMP UPb in zircon ages and SmNd data provide evidence in the West Pilbara which demonstrates that subduction-related and tectonic-accretion processes at the western margin of that ancestral continent between 3.15-2.78 Ga were coeval with, and genetically related to, crustal-scale tectonics and basin formation inboard of that margin. The tectonic division of the West Pilbara is defined by integrated tectonic analyses, geochronology, geochemistry and isotopic analyses. Geochronological studies clearly indicate that the western Pilbara comparises two domains with different recorded geohistories, whereas geochemistry and isotopic systematics reflect the changing tectonic regimes through time. In combination, these studies allow the development of a reconstruction of the relative positions of the domains through time on the western margin of the Pilbara Block. The supracrustal rocks of the northern Roebourne Lithotectonic Complex (Domain 6 in a Pilbarawide scheme) were formed in an island arc setting, facing an ocean to the north-west, prior to 3260 Ma, the time of emplacement of voluminous granitoids into the complex. In contrast, the supracrustal rocks of the southern Sholl Belt (Pilbara Domain 5) were formed in a back-arc setting behind a north-west-facing arc between 3125 and 3112 Ma, with more-or-less synchronous granite emplacement at about 3115 Ma. The two domains were tectonically juxtaposed, between 2991 and 2925 Ma, by the Sholl Shear Zone, a largely sinistral shear zone, with subsequent volcanism in both domains to about 2925 Ma. The Roebourne Lithotectonic Complex (Domain 6) is interpreted to be an allochthonous terrane, which formed north-east relative to its present position, but indigenous to the Pilbara Block rather than an exotic terrane. The East Pilbara is interpreted to have acted as a cratonic hinterland during the convergent margin tectonics that affected the two West Pilbara domains.

LATEST Archaean and earliest Palaeoproterozoic times (from 2.6 to 2.2 billion years ago) have generally been viewed as a largely quiescent period of Earth history; the geological record indicates the very slow deposition of pelagic and chemical sediments1,2, and bears only a limited record of magmatic and tectonic activity3–5. Such quiescence is consistent with the contention that the Earth's main banded iron formations (BIFs)—finely laminated chemical sedimentary rocks, rich in iron oxide—formed slowly as oxygen abundances in the oceans gradually increased, thus reducing the capacity of sea water to retain dissolved iron6–10. Here we show that a large igneous province, comprising >30,000km3 of dolerite, basalt and rhyolite, accompanied deposition of a Hamersley Province BIF 2,449 ±3 million years ago. This observation indicates that Hamersley BIFs formed during a major tectono-magmatic event and were deposited very much faster than previously thought, at similar rates to (or faster than) modern pelagic sediments. Thus the largest Palaeoproterozoic BIFs, rather than simply reflecting a gradual increase in the oxygen content of the oceans during a period of tectonic quiescence, are more likely to have formed as a result of an increased supply of suboxic iron- and silica-rich sea water upwelling onto continental shelves during a pulse (or pulses) of increased submarine magmatic and hydrothermal activity.